The present invention pertains to a process for preparing substrates having a polyurethane backing which process employs applying a frothed polyurethane forming composition to said substrate and to the resultant polyurethane foam backed substrates.
Substrates, particularly carpet substrates, have been backed with polyurethane foam as described in U.S. Pat. Nos. 3,755,212, Dunlap and Parrish; 3,821,130, Barron and Dunlap; and 3,862,879, Barron and Dunlap wherein the frothed polyurethane forming composition does not contain a silicone surfactant and in U.S. Pat. Nos. 3,706,681, Bachura; 3,849,156, Marlin et al; 3,836,560, 3,947,386, 3,957,842, 4,022,722 and 4,022,941, Prokai et al wherein the frothed polyurethane forming compositions contain a silicone surfactant.
The process of the present invention therefore provides for the preparation of frothed polyurethane backed substrates which have fine cells and excellent stability during processing. Furthermore, the process of the present invention incorporates novel low amounts of (a) silicone surfactant(s) (stabilizer), and (b) improved esthetics and cost over the same polyurethane backed substrate without the silicone surfactant (non-stabilized). It is known that penetration weight (weight of the polyurethane composition absorbed by the substrate) is dependent upon several factors, including type of substrate, component reactivity, temperature and component viscosity. Penetration weight on the commercially available carpet described in this invention had at least about 25% reduction compared to non-stabilized formulations. The reduced penetration and improved stability has resulted, on the average, in a 20% improvement in gauge (thickness of foam) over non-stabilized formulations. Cost to the customer has been effectively reduced by the process of this invention because a product (foam backed substrate) is obtained that has the same thickness employing less components by weight. In other terms, the same weight of froth is applied to the back of the substrate and a desirably thicker foam is obtained.
It is well known in the art that the frothing or mechanical whipping operation of the polyurethane forming composition is performed in high shear equipment such as a Hobart mixer, Firestone mixer, Oakes mixer and similar known equipment. The air or other inert gas should be introduced into the polyurethane forming mixture and whipped under pressure in order to obtain a workable froth. The mechanical whipping operation is conducted such that the pressure at the mixer head outlet is in the range from about 85 to about 200 psig, preferably from 85 to 150 psig.
In those processes where there is no silicone surfactant present, the substrates absorb an inordinate amount of polyurethane forming components thereby resulting in too much absorption beyond what is necessary for tuftbinding. A loss of gauge and a destabilization line at the substrate/foam interface occurs, wherein the cell structure becomes coarse and unappealing. The loss of gauge and destabilization line are esthetically unappealing to the buyer and results in higher costs to the vendor. The solution to this without a silicone is a high catalyst level or quick reaction time, which severely limits processing latitude.
In those processes wherein a silicone surfactant is employed, large quantities of the silicone surfactant are required in order to obtain fine cells or else stability of the polyurethane forming froth is not sufficient to give a fine celled foam or prevent an inordinate amount of penetration (absorption). In the present invention, a large quantity of surfactant (&gt;0.5 part) limits the processing of the froth because froth viscosity is too high to be adequately processed onto the back of a substrate such as a carpet and the pressure in the mixer head may exceed the working limit of 200 psig. Also, in the present invention, the improvement in penetration and gauge is no longer measurable from greater than about 0.3 parts surfactant. There is no real advantage, therefore, to using surfactant levels above about 0.5 parts from a processing or cost standpoint.